Octogenarians Face Higher 90-day Medical Risk but Lower 1-year Revision Rates After Primary Total Knee Arthroplasty.

BACKGROUND: Prior studies evaluating age-related outcomes after total knee arthroplasty (TKA) have examined medical complications and revision risk separately. We asked whether octogenarians have higher rates of 90-day medical complications, 30- and 90-day readmissions, and all-cause and etiology-specific revision after primary TKA. MATERIALS AND METHODS: PearlDiver all-payer claims (2010 to 2022) identified isolated, first-instance unilateral primary TKA, excluding index revision, fracture/malignancy, concomitant other-joint arthroplasty, staged/simultaneous bilateral TKA within 30 days, and prior arthroplasty within 1 year. Patients were stratified by age (<65, 65 to 79, 80 to 89 years). Outcomes included 90-day medical complications, 30- and 90-day readmissions, and 1-year all-cause and etiology-specific revision (ie, prosthetic joint infection, mechanical loosening, instability/dislocation, periprosthetic fracture). Multivariable logistic and Cox regression adjusted for sex, Elixhauser Comorbidity Index, and body mass index. RESULTS: Among 376,914 TKAs with complete covariate data, octogenarians had higher adjusted odds of 90-day medical complications and 30- and 90-day readmissions (P < .0001). Patients <65 years had the highest 1-year all-cause revision and higher adjusted odds of all-cause revision, prosthetic joint infection, and mechanical loosening or instability/dislocation revision, whereas octogenarians had a higher hazard of revision for periprosthetic fracture (P < .05). CONCLUSION: Octogenarians experienced greater early medical morbidity but lower observed 1-year revision hazards than did younger patients. These findings support age-calibrated counseling emphasizing perioperative optimization in older patients while informing younger patients of their greater early revision risk. Because mortality was unavailable as a competing event, lower revision hazards in octogenarians should be interpreted cautiously and not assumed to reflect superior implant durability. Future studies incorporating competing-risk methodology, frailty measures, and patient-reported outcomes are needed.